Māhukona is a submerged shield volcano

Shield volcano

A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...

 on the northwestern flank of the Island of Hawaii

Hawaii (island)

The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...

. A drowned coral reef at about 3,770 feet (-1,150 m) below sea level and a major break in slope at about 4,400 feet (-1,340 m) below sea level represent old shorelines. The summit of the shield volcano was once 800 feet (250 m) above sea level. It has now subsided below sea level. A roughly circular caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 marks the summit of Māhukona. A prominent rift zone

Rift zone

A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...

 extends to the west. A second rift zone probably extended to the east but has been buried by younger volcanoes. The main shield-building stage of volcanism ended about 470,000 years ago. The summit of the shield volcano subsided

Subsidence

Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...

 below sea level between 435,000 and 365,000 years ago.
This makes Māhukona the oldest volcano to build Hawaii island, compared to Kohala

Kohala (mountain)

Kohala is the oldest of five volcanoes that make up the island of Hawaii. Kohala is an estimated one million years old—so old that it experienced, and recorded, a reversal of magnetic field 780,000 years ago. It is believed to have breached sea level more than 500,000 years ago and to...

 to the east and Hualālai

Hualalai

Hualālai is a dormant shield volcano on the island of Hawaii in the Hawaiian Islands. It is the third-youngest and the third most active of the five volcanoes that form the island of Hawaii, following Kīlauea and the much larger Mauna Loa, and also the westernmost. Its peak is above sea...

 to the southeast.

An aftershock of the 2006 Hawaii earthquake

2006 Hawaii earthquake

The 2006 Hawaii earthquake was an offshore earthquake occurring southwest from Puakō and north of Kailua-Kona, Hawaii, just offshore of the Kona Airport, on Sunday October 15, 2006 at 7:07:49 AM local time . It measured 6.7 on the moment magnitude scale, and was located at , at a depth of...

 of magnitude

Moment magnitude scale

The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

 6 hit about seven minutes after the main shock just to the south.
The Monterey Bay Aquarium Research Institute

Monterey Bay Aquarium Research Institute

The Monterey Bay Aquarium Research Institute is a not-for-profit oceanographic research center in Moss Landing, California affiliated with the Monterey Bay Aquarium. It was founded in 1987 by David Packard of Hewlett-Packard fame...

 investigated the area with a remotely controlled submarine in 2001.

It was named for the area known as Māhukona

Mahukona, Hawaii

Māhukona is a former settlement on the island of Hawaii. The extinct submerged volcano Māhukona, off shore and to the south, is named for this area. It was once the terminus of the Hawaiian Railroad.-History:...

on the shore to the northeast.